Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been already put to practical use as batteries for small electronic devices such as notebook computers, cellular phones and the like because of their advantages of high energy density, small self-discharge, excellent long-term reliability and the like. In recent years, the use of batteries has been expanded to electric vehicles, home storage batteries or power storages.
A lithium ion secondary battery is mainly composed of a positive electrode containing a positive electrode active material, a negative electrode containing a material capable of absorbing and desorbing lithium ions as a main component and a non-aqueous electrolyte solution. As a positive electrode active material used for the positive electrode, for example, lithium metal oxides such as LiCoO2, LiMnO2, LiNiO2, LiFePO4, LiMn2O4 are used.
As a negative electrode active material used for a negative electrode, metallic lithium, silicon, oxides such as silicon oxide, and carbon materials, which are capable of absorbing and desorbing lithium ions, are used. In particular, a lithium ion secondary battery using a carbon material such as graphite (artificial graphite, natural graphite), coke capable of absorbing and desorbing lithium ions, has already been put to practical use.
On the other hand, non-aqueous electrolyte solutions that have been used are those containing a mixed solvent of cyclic carbonate-based solvents such as ethylene carbonate, propylene carbonate and the like, and open-chain carbonate-based solvents such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like, and a lithium salt such as LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, lithium bis(oxalate)borate (LiB(C2O4)2).
In a secondary battery using these non-aqueous electrolyte solutions, for example, particularly under high temperature, the solvent in the electrolyte solution undergoes a reductive decomposition on a surface of the negative electrode, and the decomposition product deposited on the surface of the negative electrode causes an increase in resistance, or gas generated by the decomposition of the solvent causes swelling of the battery. In addition, on a surface of the positive electrode, the solvent undergoes oxidative decomposition, and the decomposition product deposited on the surface of the positive electrode causes an increase in resistance, or gas generated by the decomposition of the solvent causes swelling of the battery. As a result, at high temperature, storage characteristics of batteries are lowered or cycle characteristics of secondary batteries are lowered, leading to a problem of lowering of the battery characteristics.
In order to prevent these problems from occurring, it has been attempted to add in the non-aqueous electrolyte solution a compound having a function of forming a protective coating. Specifically, it has been known that the decomposition of a compound added to the electrolyte solution at the surface of the electrode active material is promoted intentionally during the initial charging, and that the decomposition product forms a protective coating, i.e. SEI (Solid Electrolyte Interface), having a protection function for preventing the degradation of further fresh solvent. It has been reported that the protective coating thus formed suppresses properly a chemical reaction or decomposition of the solvent at the electrode surface, and as a result, is effective to maintain the battery characteristics of the secondary battery (non-Patent Document 1).
As the protective film-forming additive, for example, it has been attempted to add vinylene carbonate or maleic anhydride in the electrolyte solution to improve the battery characteristics (non-patent document 1).
Also, a technology using a sulfonic acid ester-based compound has been also proposed, namely the use of benzenesulfonic acid ester derivatives (Patent Documents 1 and 2) and dioxadithiepin tetraoxide derivatives (Patent Document 3) has been disclosed.